Method for electroplating titanium



2,829,091 METHOD FOR ELEQTRQPLATING TITANIUM Leo Missal, North Hollywood, Calif., assignor to Menasco Manufacturing Company, Burbank, Calif., a corporation of California No Drawing. Application June 4, 1956 Serial No. 588,972

9 Claims. (Cl. 204-32) This invention relates to the metal coating art, and has particular reference to a process and composition for treating the surfaces of titanium and titanium alloys to permit subsequent treatment, such as electroplating, of the same.

Titanium and titanium alloys are finding increasing uses and applications, particularly in'the aircraft industry, due primarily to the excellent strength-weight ratios of the metal and its alloys. However, these materials exhibit tendencies toward galling, seizing and-excessive wear when utilized in applications requiring'motion between components such as in bearings, sliding assemblies and the like.

One of the principal objects of this invention is, therefore, to provide a process for the treatment of titanium and its alloys to permit the application thereto of a hard metal coating having satisfactory bearing characteristics.

Another object of this invention is to provide a process for the treatment of surfaces of titanium and titanium alloys to permit the electroplating thereon of metallic films having'characteristics of adhesion, hardness, electrical conductivity, solderability, etc., comparable to films produced on common metals by conventional methods.

Another object of this invention is to provide a'process for chromium plating the surfaces of titanium and titanium alloys.

Another object of this invention is to provide a process for chromium plating many different types of titanium alloys. I 9

Other objects and advantages'of this invention, it is believed, will be readily apparent from the following detailed description of preferred embodiments thereof.

Briefly, this invention includes the discovery that articles of titanium and titanium alloys may be treated with aqueous solutions of mixtures of hydrofluoric acid and chromic acid or its salts to render the surfaces of the articles receptive" to subsequent electrolytic plating thereof to produce an adherent plate of chromium or other metals. 7

The following are specific examples of processes and compositions embodying the present invention, but it is to be understood that it is not intended to limit the invention to the specific steps set forth therein.

Example 1 7 Parts forged of a titanium alloy containing 4% aluminum and 4% manganese were cleaned with a conventional degreasing agent, rinsed and then immersed in an acid etch bath consisting of three parts by volume of 69% nitric acid andone part by volume of 60% hydrofluoric acid for a sufiicient length of time at room temperature to chemically clean and activate the titanium surface (about 1 minute). While best results are obtained with the described mixture, other acids such as sulfuric, hydrochloric mixed withhydrofluoric acid, or hydrofluoric acid alone may be used.

The next step was to rinse the parts from the acid cleaning bath with distilled water, and they were then dipped into a chemical'treatment bath for a period of about minutes, the temperature of the bath being maintained at about 190 F. The bath comprised an aqueous (distilled water) solutionof the following ingredients in the proportions indicated:

Example 1a Hydrofiuoric acid (60% HF) ml./liter Sodium dichromate (Na Cr O .2H O) gm./liter 250 The parts were removed from this bath and rinsed thoroughly in cold running tap water. The parts were then chromium plated in a conventional hard chrome electroplating bath at 3 amperes per square inch for 4 hours, the bath temperature being maintained at 130 F. The plating solution consisted of 33 oz./ gal. of chromic acid and 0.33 oz./gal. of sulfate ion.

Example 1 b The identical process of Example 1 and the treatment bath of Example 3a below were utilized in chrome plating parts of a titanium alloy containing 5% chromium and 3% aluminum.

Example 3a Hydrofiuoric acid HF) rnl./ liter, 25 Sodium dichromate (Na cr O lH O) .gm./liter 400 The bath of Example 3a comprised an aqueous distilled water) solution of the'above ingredients.

Excellent plating results were obtained with theprocess of the above examples. The adherence of the chromium plate under steel ball indentation tests and under specially designed bearingload tests was exc ellent and qualified the parts for use in heavy duty aircraft landing gear assemblies. v a i T The chemical reactions and/ or physical phenomena involved in the treatment with the chemical treatment bath of Example 111' are not'entirely understood. 'It would appearyhowever, that the hydrofluoric acid in the bath plays an important part in the complete removal of the oxide film. It should be noted that the hydrofluoric acid may be formed in situ by the addition of a water-soluble salt of hydrofluoric acid and another acid, such as for example, sulfuric,'hydrochloric, phosphoric, citric, etc.

The inclusion of the dichromate in the composition of Example la is also an important feature of the invention. It has been found that the dichromate makes possible a chromium plate which meets the requirements for heavilyloaded bearing surfaces. I It' is believed that this is due, in partat least, tothe fact that the dichromate, in conjunction with the hydrofluoric acid, activates, or renders 'with, the sodium dichromate of. Example la.

For obtaining maximum adherence, the concentration of the chromic compound in the treatment solution is critical and should be maintained above about 15% by weight. Optimum results with the alloy of Example 1 plating said articles in a plating solution.

were obtained utilizing concentrations of sodium dichromate from 200 gm./liter to 400 gm./liter at a 60% hydrofluoric acid concentration of 50 mL/liter. At a dichromate concentration of 250 gm./liter, 60% hydrofluoric acid concentration .of 25 ml./liter to 75 ml./liter gave excellent chrome plate adhesion with a 20-minute immersion time, and concentrations of 37.5 ml./litcr to 62.5 ml./liter of 60% hydrofluoric acid gave excellent adhesion with a 10-minute immersion time.

With the alloy of Example 2, concentrations of 200 to 300 gm./liter of sodium dichromate and 50 ml./liter of 60% hydrofluoric acid at 10 and 20-minute immersion times gave excellent results. At a dichromate concentration of 200 gm./liter, 35 to 60 ml./liter of 60% hydrofluoric acid gave excellent results with a 20-minute immersion, While at 10 minutes, the hydrofluoric acid range was extended to 25 to 60 ml./ liter.

With the alloy of Example 3, excellent results were obtained utilizing somewhat higher concentrations of sodium dichromate and lower concentrations of hydrofluoric acid. At a level of 400 gin/liter of dichromate, adherent chromium plate was obtained with 15-35 ml./ liter of 60% hydrofluoric acid under immersion times of 10 and 20 minutes.

As indicated above, the proportions of the ingredients of Examples 10 and 3a may be varied, depending primarily upon the type of alloy and the treating time, and the relative proportions of the two ingredients. From a standpoint of commercial practicability, the concentration ranges are approximately as follows:

Hydrofluoric acid 05-20% (by weight as anhydrous HF) Chromic acid or soluble salt thereof 15 by weight to saturation point. Water Balance.

The temperature of the chemical treatment bath is preferably maintained within the range of about 180 to the boiling point, but lower temperatures, within reasonable limits, may be utilized. For best results at the temperatures indicated, the immersion time is at least five minutes, preferably from -20 minutes, and may be substantially longer.

It will be readily understood by those skilled in the art thatthe process and composition of this invention are not limited to the chromium plating operation. For example, parts treated as described may be given a copper plating from a conventional acid copper bath,.or may be plated with any other conventional metal.

Having fully described my invention, it is to be understood that I do not wish to. be limited to the details set forth, but my invention is of the full scope of the appended claims.

I claim:

1. A process for treating the surfaces of articles of titanium and titanium base alloys, including the steps of immersing said articles in a bath consisting essentially of an aqueous solution of 0.5% to about 20% by weight of hydrofluoric acid, and. from about by weight to the saturation point of a chromium compound selected from the group consisting of chromic acid and its salts, and electroplating said articles in a plating solution.

2. A process for treating the surfaces of articles of titanium and titanium base alloys, including the. steps of immersing said articles in a bath consisting essentially of an aqueoussolution of 0.5% to about'20% by weight of hydrofluoric acid, and from about 15% by weight to the saturation point of sodium dichromate, and electro- 3. A process for treating the surfaces of articles of titanium and titanium base alloys, including the steps of immersing saidarticles in a bath consisting essentially of an aqueous solution of about 3% by Weight of hydrofluoric acid, and from about to about 40% by weight of a chromium compound selected from the group consisting of chromic acid and its salts, and electroplating said articles in a plating solution.

4. A process for treating the surfaces of articles of titanium and titanium base alloys, including the steps of immersing said articles in a bath consisting essentially of an aqueous solution of about 3% by Weight of hydrofluoric acid, and from about 20% to about by weight of sodium dichromate, and electroplating said articles in a plating solution.

5. A process for treating the surfaces of articles of titanium and titanium base alloys, including the steps of immersing said articles in a bath consisting essentially of an aqueous solution of 0.5% to about 20% by Weight of hydrofluoric acid, and from about 15% by weight to the saturation point of a chromium compound selected irom the group consisting of chromic ac d and its salts, maintaining the temperature of said bath at about F. to the boiling point for 10-20 minutes, removing said articles and rinsing the same, and electroplating said articles in a plating solution.

6. A process for treatingthe surfaces of articles of titanium and titanium base alloys, including the steps, in sequence, of cleaning said articles in an acid etch bath, immersing said articles in a bath consisting essentially of an aqueous solution of 0.5% to about 20% by Weight of hydrofluoric acid, and from about 15% by Weight to the saturation point of a chromium compound selected from the roup consisting of chromic acid and its salts, and electroplating said articles in a plating solution.

7. A process for treating the surfaces of articles of titanium and titanium base alloys, including the steps, in sequence, of cleaning said articles in an acid etch bath, immersing said articles in a bath consisting essentially of an aqueous solution of 0.5% to about 20% by Weight of hydrofluoric acid, and from about 15 by weight to the saturation point of sodium dichromate, and electroplating said articles in a plating solution.

8. A process for treating the surfaces of articles of titanium and titanium base alloys, including the steps, in sequence, of cleaning said articles in an acid etch bath, immersing said articles in a bath consisting essentially of an aqueous solution of about 3% by Weight of hydrofluoric acid, and from about 20% to about 40% by Weight of sodium dichromate, and electroplating said articles in a plating solution,

9. A process for treating the surfaces of articles of titanium and titanium base alloys, including the steps, in sequence, of cleaning said articles in an acid etch bath, immersing said articles in a bath consisting essentially of w an aqueous solution of 0. 5% to about 20% by Weight of hydrofluoric acid, and from about 15 by weight to the saturation point of sodium dichromate, maintaining the temperature of said bath at about 180 F. to the boiling point for 10-20 minutes, removing said articles and rinsing the same, and electroplating said articles in a plating solution.

References Cited in the file of this patent UNITED STATES PATENTS 1,544,451 Hambuechen June 30, 1925 1,978,791 Hale Oct. 30, 1934 2,127,640 Brown Aug. 23, 1938 2,171,546 Kapps Sept. 5, 1939 2,311,623 Blackmun et al. Feb.23, 1943 2,471,909 Spruance May 31, 1949 2,478,171 MacPherson Aug. 9, 1949 2,507,956 Bruno et al. May 16, 1950 2,711,364 Beach June 21, 1955 2,734,837 Hands Feb. 14, 1956 2,764,538 Smart Sept. 25, 1956 OTHER REFERENCES Handbook on Titanium Metal, 7th ed., August 1, 1953, Titanium Metals Corporation, New York, pp. 92-93. 

5. A PROCESS FOR TREATING THE SURFACES OF ARTICLES OF TITANIUM AND TITANIUM BASE ALLOYS, INCLUDING THE STEPS OF IMMERSING SAID ARTICLES IN A BATH CONSISTING ESSENTIALLY OF AN AQUEOUS SOLUTION OF 0.5% TO ABOUT 20% BY WEIGHT OF HYDROFLUORIC ACID, AND FROM ABOUT 15% BY WEIGHT TO THE SATURATION POINT OF A CHROMIUM COMPOUND SELECTED FROM THE GROUP CONSISTING OF CHROMIC ACID AND ITS SALTS, MAINTAINING THE TEMPERATURE OF SAID BATH AT ABOUT 180*F. TO THE BOILING POINT FOR 10-20 MINUTES, REMOVING SAID ARTICLES IN A PLATING SOLUTION. 